This invention relates to die casting or injection molding and in particular to a device for venting the cavities of the molds in such machines during the operative cycles thereof to reduce as much as possible the porosity in the finished castings or molded articles.
In the operation of a die casting machine for example, molten zinc or other casting metal is shot into the mold cavity of the machine and the molten metal has to displace air or other gases in the cavity. Conventionally, gas is allowed to escape from the cavities through the provision of a plurality of small channels provided along the parting line of the dies and positioned at locations where the entrapment of gas is most likely to take place. However, conventional methods have not been entirely successful in reducing porosity in the finished castings caused by air or other gases entrapped in the cavity when the molten metal solidifies.
There have been some attempts to improve on the abovementioned conventional method by providing some form of venting apparatus where a valve in the apparatus remains open while the gas in the cavity escapes, being pushed out by the advancing molten metal. When the metal enters the device the valve is closed. One example of this is shown in German Offenlegungsschrift 27 51 431 to Fritz Hodler or in U.S. Pat. No. 3,885,618 to Hodler. Still further examples of ventilation ducts in molding machines are to be found in U.S. Pat. Nos. 3,892,508 of July 1st, 1975, 3,433,291 of Mar. 18th, 1969, 3,349,833 of Oct. 31st, 1967, 2,971,230 of Feb. 14th, 1961 and U.S. Pat. No. 3,991,971 of Nov. 16th, 1976.
All of the abovementioned devices include at least several moving parts which, in time, wear out and fail to perform as designed. Moreover, because of the moving parts, the manufacturing costs are substantial.
The present invention provides a substantial advance in the art by providing a device which permits a substantially larger venting of mold cavities over and above conventional vending means and in which no moving parts are used.